Lubricating composition

ABSTRACT

Lubricating composition for use in the crankcase of an engine comprising: (i) a base oil comprising at least one monoester or a mixture of monoesters, wherein said monoester or mixture of monoesters has a kinematic viscosity at 100° C. of not more than 4 mm 2 /s, a viscosity index of at least 130 and a Noack evaporation loss of not more than 20 wt %; and (ii) a polymeric viscosity index improvers selected from (a) one or more comb polymers; (b) a poly(meth)acrylate polymer having 1 to 70 mol % of one or more (meth)acrylate structural units represented by formula (1) below (1) wherein R 1  is a hydrogen atom or a methyl group, and R 2  is a straight chain or branched hydrocarbon group having not less than 16 carbon atoms; (c) styrene-diene hydrogenated copolymers; and (d) mixtures thereof. The lubricating composition of the present invention provides improved fuel economy properties.

FIELD OF THE INVENTION

The present invention relates to a lubricating composition for use in the crankcase of an engine for providing improved fuel economy.

BACKGROUND OF THE INVENTION

Government regulations and market demands continue to emphasize conservation of fossil fuels in the transportation industry. There is increasing demand for more fuel-efficient vehicles in order to meet CO₂ emissions reductions targets. Therefore, any incremental improvement in fuel economy (FE) is of great importance in the automotive sector. Lubricants can play an important role in reducing a vehicle's fuel consumption and there is a continuing need for improvements in fuel economy performance of lubricant compositions contained within an internal combustion engine.

Various attempts have been made to improve the fuel economy performance of lubricating engine oils. One technique for improving fuel economy performance is to reduce the kinematic viscosity and to improve the viscosity index of products, i.e. multigrading, by combining reduction of base oil viscosity and addition of viscosity index improvers. There are many viscosity modifiers and base oils that can be used to blend, for example, 0W-20 formulations. However, it is not possible to achieve a very high VI and acceptable volatility with conventional combinations of viscosity modifiers and base oils.

US2010/0190671 relates to the use of comb polymers for reducing fuel consumption. In particular, the comb polymer disclosed therein comprises, in the main chain, at least one repeat unit which is obtained from at least one polyolefin-based macromonomer, and at least one repeat unit which is obtained from at least one low molecular weight monomer selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl(meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group and mixtures thereof, where the molar degree of branching is in the range of 0.1 to 10 mol % and the comb polymer comprises a total of at least 80% by weight, based on the total weight of repeat units of the comb polymer, of the at least one repeat unit which is obtained from the at least one polyolefin-based macromonomer and the at least one repeat unit which is obtained from the at least one low molecular weight monomer.

US2011/0124536 relates to a lubricant composition comprising (A) a lubricant base oil consisting of, based on the total amount of said base oil, 50 to 99.9 mass % of a lubricant base oil having a 100° C. kinematic viscosity of not less than 1 and less than 5 mm²/s, and 0.1 to 50 mass % of a lubricant base oil having a 100° C. kinematic viscosity of 5 to 200 mm²/s, and (B) a viscosity index improver having a weight average molecular weight of not less than 10000, and a ratio of the weight average molecular weight to a PSSI of not lower than 0.8×10⁴, wherein said composition comprises 0.1 to 50 mass % of said VI improver (B) based on a total amount of the composition, and wherein said composition has a 100° C. kinematic viscosity of 3 to 15 mm²/s, and a ratio of a 150° C. HTHS viscosity to a 100° C. HTHS viscosity of not less than 0.50.

WO2009/130445 discloses engine lubricants, particularly to engine lubricants for use in four-stroke engines, comprising at least one monoester and not more than 20 wt % of additives, wherein said at least one monoester, or mixture of said monoesters if more than one is present, has a kinematic viscosity at 100° C. of not more than 3.3, a viscosity index of at least 130 and a Noack evaporation loss of not more than 15 wt %.

There is a need to provide lubricating compositions for use in the crankcase of an engine, wherein the compositions provides high VI, low viscosity and acceptable volatility properties, as well as improved fuel economy benefits.

SUMMARY OF THE INVENTION

According to the present invention there is provided a lubricating composition for use in the crankcase of an engine comprising:

-   (i) a base oil comprising at least one monoester or a mixture of     monoesters, wherein said monoester or mixture of monoesters has a     kinematic viscosity at 100° C. of not more than 4 mm²/s, a viscosity     index of at least 130 and a Noack evaporation loss of not more than     20 wt %; and -   (ii) a polymeric viscosity index improvers selected from     -   (a) one or more comb polymers;     -   (b) a poly(meth)acrylate polymer having 1 to 70 mol % of one or         more (meth)acrylate structural units represented by formula (1)         below

-   -   -   wherein R¹ is a hydrogen atom or a methyl group, and R² is a             straight chain or branched hydrocarbon group having not less             than 16 carbon atoms;

    -   (c) styrene-diene hydrogenated copolymers; and

    -   (d) mixtures thereof.

The lubricating composition of the present invention provides high VI, low viscosity and acceptable volatility properties in addition to improved fuel economy.

DETAILED DESCRIPTION OF THE INVENTION

The base oil comprises at least one monoester or a mixture of monoesters, wherein said monoester or mixture of monoesters has a kinematic viscosity at 100° C. (as measured by ASTM D445) of not more than 4 mm²/s, preferably not more than 3.3 mm²/s, a viscosity index of at least 130 (as calculated by ASTM D2270) and a Noack evaporation loss (as measured by ASTM D5800) of not more than 20 wt %, preferably not more than 15 wt %.

Said monoester or mixture of said monoesters is preferably present in the lubricating composition at a total level of at least 10 wt %, more preferably at least 20 wt %, most preferably at least 30 wt %, by weight of the lubricating composition. Said monoester or mixture of said monoesters is preferably present in the lubricating composition at a total level of at most 75 wt %, more preferably at most 50 wt % and even more preferably at most 40 wt % of said at least one monoester.

While not wishing to be limited by theory, the present invention relies upon the low viscosity, low volatility monoester or mixtures of monoesters to facilitate a lower base oil blend viscosity having acceptable volatility. This lower base oil blend viscosity means that more polymeric viscosity index improver is needed to achieve the required HTHS 150 viscosity (High Temperature High Shear viscosity at 150° C.) (according to ATSM D4683). A greater level of polymeric VI improver will provide a high viscosity index (VI) and a lower HTHS 100 viscosity (High Temperature High Shear viscosity at 100° C.) (as measured by ASTM D6616) for the same HTHS 150 viscosity. Essentially, the viscosity will change less with temperature. As an engine operates closer to 100° C. than 150° C., the lubricant is thinner under operating conditions and therefore delivers improved fuel economy. Addition of the monoester or mixtures of monoesters and the resulting lower base oil blend viscosity, with acceptable volatility, will mean that whatever polymeric viscosity index improver is chosen, more of the polymer will be needed. Therefore, the VI will be higher and the HTHS 100 lower than that of the corresponding formulation without the monoester or mixture of monoesters. Therefore inclusion of the monoester or mixture of monoesters helps to improve fuel economy whichever polymeric viscosity index improver is chosen.

The selected polymeric viscosity index improvers used in the present invention having optimised architecture, such as the Viscoplex 3-201 comb polymer from Evonik Industries and the Aclube V-5110 alkyl(meth)acrylate copolymer supplied by Sanyo Chemicals, will provide a higher VI for a given increase in viscosity, and therefore the benefit will be higher for these selected polymers.

Preferably, said at least one monoester is the reaction product of a monohydric alcohol and a monocarboxylic acid wherein said monohydric alcohol is at least one saturated branched-chain aliphatic monohydric alcohol having between 16 and 36 carbon atoms and wherein said monocarboxylic acid is at least one saturated straight-chain aliphatic monocarboxylic acid having between 5 and 10, preferably between 5 and 7 carbon atoms. If desired, mixtures of said alcohols and/or said acids may be used in the esterification reaction.

Alternatively, said at least one monoester is the reaction product of a monohydric alcohol and a monocarboxylic acid wherein said monohydric alcohol is at least one saturated straight-chain aliphatic monohydric alcohol having between 5 and 7 carbon atoms and wherein said monocarboxylic acid is at least one saturated branched-chain aliphatic monocarboxylic acid having between 16 and 36 carbon atoms. If desired, mixtures of said alcohols and/or said acids may be used in the esterification reaction.

Mixtures of the monoesters described above may also be used.

In a preferred embodiment, the monoesters used in the present invention are monoesters which are the reaction products of said branched-chain alcohols having between 16 and 36 carbon atoms and said straight-chain acids having between 5 and 10, preferably between 5 and 7, carbon atoms as described above.

The branched-chain monohydric alcohol may be obtained from any suitable source and typically may be selected from Guerbet alcohols, oxo alcohols, aldol condensation derived alcohols and mixtures thereof.

More especially, the branched-chain monohydric alcohol is an alcohol branched at the β position on the main carbon chain. Typically, such alcohols may be selected from 2-octadecanol-1, 2-heptylundecanol-1, 2-octadodecanol-1, 2-nonyltridecanol-1 and 2-decyltetradecanol-2, and mixtures of two or more such alcohols. Such alcohols are conveniently Guerbet alcohols.

Preferably, the branched-chain monohydric alcohol is at least one alcohol having between 16 and 28 carbon atoms, more preferably between 20 and 24 carbon atoms.

The straight-chain monocarboxylic acid may be obtained from any suitable source and is selected from pentanoic acid (valeric acid), hexanoic acid (caproic acid), heptanoic acid (enanthic acid), octanoic acid (caprylic acid), decanoic acid (capric acid) and mixtures of two or more such acids.

Preferably, said at least one monoester has a kinematic viscosity at 100° C. (as measured by ASTM D445) of not more than 3.0 mm²/s. Preferably said at least one monoester has a viscosity index (as measured by ATSM 2270) of at least 140. Preferably, said at least one monoester has a pour point (according to ASTM D97) of not more than −30° C., more preferably not more than −35° C. and especially not more than −40° C. Preferably, said at least one monoester has a Noack evaporation loss (according to ATSM D5800) of not more than 17 wt %, more preferably not more than 15.0 wt %.

Preferably, said at least one monoester has a flash point (according to Cleveland Closed Cup method) of at least 200° C., more preferably at least 210° C. and more particularly at least 220° C.

Preferably, said at least one monoester has a non-polarity index (NPI), as described in EP-B-0792334 of at least 80, preferably at least 90.

Preferably, said at least one monoester has a cold crank simulation (CCS) dynamic viscosity (according to ASTM D5293) at −35° C. of not more than 6200 cPs.

Examples of suitable monoesters and mixtures of monoesters for use herein include those disclosed in WO2009/130445.

Examples of commercially available monoesters for use herein include Priolube 1544 commercially available from Croda International Plc.

In the lubricating compositions of the present invention, the base oil may comprise one or more additional base oils, in addition to the one or more monoesters or mixtures of monoesters described hereinabove. There are no particular limitations regarding the additional base oils which can be used in the lubricating composition of the present invention and various conventional mineral oils, synthetic oils as well as naturally derived esters such as vegetable oils may be conveniently used.

The base oil used in the present invention may conveniently comprise mixtures of one or more mineral oils and/or one or more synthetic oils; thus, according to the present invention, the term “base oil” may refer to a mixture containing more than one base oil. Mineral oils include liquid petroleum oils and solvent-treated or acid-treated mineral lubricating oil of the paraffinic, naphthenic, or mixed paraffinic/naphthenic type which may be further refined by hydrofinishing processes and/or dewaxing.

Suitable base oils for use in the lubricating oil composition of the present invention are Group I-III mineral base oils (preferably Group III), Group IV poly-alpha olefins (PAOs), Group II-III Fischer-Tropsch derived base oils (preferably Group III), Group V ester base oils, and mixtures thereof.

By “Group I”, “Group II” “Group III” and “Group IV” and “Group V” base oils in the present invention are meant lubricating oil base oils according to the definitions of American Petroleum Institute (API) for categories I, II, III, IV and V. These API categories are defined in API Publication 1509, 15th Edition, Appendix E, April 2002.

A preferred base oil for use herein, in addition to the monoester or mixture of monoesters, is a Fischer-Tropsch derived base oil. Fischer-Tropsch derived base oils are known in the art. By the term “Fischer-Tropsch derived” is meant that a base oil is, or is derived from, a synthesis product of a Fischer-Tropsch process. A Fischer-Tropsch derived base oil may also be referred to as a GTL (Gas-To-Liquids) base oil. Suitable Fischer-Tropsch derived base oils that may be conveniently used as the base oil in the lubricating composition of the present invention are those as for example disclosed in EP 0 776 959, EP 0 668 342, WO 97/21788, WO 00/15736, WO 00/14188, WO 00/14187, WO 00/14183, WO 00/14179, WO 00/08115, WO 99/41332, EP 1 029 029, WO 01/18156 and WO 01/57166.

Typically, the aromatics content of a Fischer-Tropsch derived base oil, suitably determined by ASTM D 4629, will typically be below 1 wt. %, preferably below 0.5 wt. % and more preferably below 0.1 wt. %. Suitably, the base oil has a total paraffin content of at least 80 wt. %, preferably at least 85, more preferably at least 90, yet more preferably at least 95 and most preferably at least 99 wt. %. It suitably has a saturates content (as measured by IP-368) of greater than 98 wt. %. Preferably the saturates content of the base oil is greater than 99 wt. %, more preferably greater than 99.5 wt. %. It further preferably has a maximum n-paraffin content of 0.5 wt. %. The base oil preferably also has a content of naphthenic compounds of from 0 to less than 20 wt. %, more preferably of from 0.5 to 10 wt. %.

Typically, the Fischer-Tropsch derived base oil or base oil blend has a kinematic viscosity at 100° C. (as measured by ASTM D 7042) in the range of from 1 to 30 mm²/s (cSt), preferably from 1 to 25 mm²/s (cSt), and more preferably from 2 mm²/s to 12 mm²/s. Preferably, the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. (as measured by ASTM D 7042) of at least 2.5 mm²/s, more preferably at least 3.0 mm²/s. In one embodiment of the present invention, the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of at most 5.0 mm²/s, preferably at most 4.5 mm²/s, more preferably at most 4.2 mm²/s (e.g. “GTL 4”). In another embodiment of the present invention, the Fischer-Tropsch derived base oil has a kinematic viscosity at 100° C. of at most 8.5 mm²/s, preferably at most 8 mm²/s (e.g. “GTL 8”).

Further, the Fischer-Tropsch derived base oil typically has a kinematic viscosity at 40° C. (as measured by ASTM D 7042) of from 10 to 100 mm²/s (cSt), preferably from 15 to 50 mm²/s.

Also, the Fischer-Tropsch derived base oil preferably has a pour point (as measured according to ASTM D 5950) of below −30° C., more preferably below −40° C., and most preferably below −45° C.

The flash point (as measured by ASTM D92) of the Fischer-Tropsch derived base oil is preferably greater than 120° C., more preferably even greater than 140° C.

The Fischer-Tropsch derived base oil preferably has a viscosity index (according to ASTM D 2270) in the range of from 100 to 200. Preferably, the Fischer-Tropsch derived base oil has a viscosity index of at least 125, preferably 130. Also it is preferred that the viscosity index is below 180, preferably below 150.

In the event the Fischer-Tropsch derived base oil contains a blend of two or more Fischer-Tropsch derived base oils, the above values apply to the blend of the two or more Fischer-Tropsch derived base oils.

The lubricating oil composition preferably comprises 80 wt % or greater of Fischer-Tropsch derived base oil. Synthetic oils include hydrocarbon oils such as olefin oligomers (including polyalphaolefin base oils; PAOs), dibasic acid esters, polyol esters, polyalkylene glycols (PAGs), alkyl naphthalenes and dewaxed waxy isomerates.

Poly-alpha olefin base oils (PAOs) and their manufacture are well known in the art. Preferred poly-alpha olefin base oils that may be used in the lubricating compositions of the present invention may be derived from linear C₂ to C₃₂, preferably C₆ to C₁₆, alpha olefins. Particularly preferred feedstocks for said poly-alpha olefins are 1-octene, 1-decene, 1-dodecene and 1-tetradecene.

There is a strong preference for using a Fischer-Tropsch derived base oil over a PAO base oil, in view of the high cost of manufacture of the PAOs. Thus, preferably, the base oil contains more than 50 wt. %, preferably more than 60 wt. %, more preferably more than 70 wt. %, even more preferably more than 80 wt. %. most preferably more than 90 wt. % Fischer-Tropsch derived base oil. In an especially preferred embodiment not more than 5 wt. %, preferably not more than 2 wt. %, of the base oil is not a Fischer-Tropsch derived base oil. It is even more preferred that 100 wt % of the base oil is based on one or more Fischer-Tropsch derived base oils.

The total amount of base oil incorporated in the lubricating composition of the present invention is preferably in the range of from 60 to 99 wt. %, more preferably in the range of from 65 to 90 wt. % and most preferably in the range of from 70 to 85 wt. %, with respect to the total weight of the lubricating composition.

Typically the base oil (or base oil blend) as used according to the present invention has a kinematic viscosity at 100° C. (according to ASTM D445) of above 2.5 cSt and below 5.6 cSt. According to a preferred embodiment of the present invention the base oil has a kinematic viscosity at 100° C. (according to ASTM D445) of between 2.7 and 4.5 cSt. In the event the base oil contains a blend of two or more base oils, it is preferred that the blend has a kinematic viscosity at 100° C. of between 2.7 and 4.5 cSt.

Another essential component of the lubricating composition of the present invention is one or more polymeric viscosity index improvers. The lubricating composition according to the present invention comprises one or more polymeric viscosity index improvers, preferably in a solid polymer amount of from 0.1 wt % to 7 wt %, more preferably from 0.25 wt % to 5 wt %, and even more preferably from 0.5 wt % to 4 wt %, by weight of the total lubricating composition.

Preferably the polymeric viscosity index improver has a weight average molecular weight of not less than 10000 and a ratio of the weight average molecular weight to the PSSI of not less than 0.8×10⁴.

Suitable polymeric VI improvers for use herein are selected from:

-   -   (a) one or more comb polymers;     -   (b) a poly(meth)acrylate polymer having 1 to 70 mol % of one or         more (meth)acrylate structural units represented by formula (1)         below

-   -   -   wherein R⁴ is a hydrogen atom or a methyl group, and R² is a             straight chain or branched hydrocarbon group having not less             than 16 carbon atoms;

    -   (c) styrene-diene hydrogenated copolymers; and

    -   (d) mixtures thereof.

In a preferred embodiment herein, the polymeric VI improver is a comb polymer. A preferred comb polymer for use herein comprises, in the main chain, at least one repeat unit which is obtained from at least one polyolefin-based macromonomer, and at least one repeat unit which is obtained from at least one low molecular weight monomer selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl(meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having from 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group and mixtures thereof, where the molar degree of branching is in the range of 0.1 to 10 mol % and the comb polymer comprises a total of at least 80% by weight, based on the total weight of repeat units of the comb polymer, (or in another aspect based on the total weight of the comb polymer), of the at least one repeat unit which is obtained from the at least one polyolefin-based macromonomer and the at least one repeat unit which is obtained from the at least one low molecular weight monomer.

Preferably, the comb polymer used herein has 8% to 30% by weight of repeat units which are derived from polyolefin-based macromonomers, and the molar degree of branching of the comb polymer is in the range of 0.3% to 1.1%.

The term “comb polymer” as used herein means that relatively long side chains are bonded to a polymeric main chain, frequently also known as the backbone. The comb polymers for use in the present invention have at least one repeat unit which is derived from polyolefin-based macromonomers. The exact proportion is evident via the molar degree of branching. The term “main chain” as used herein does not necessarily mean that the chain length of the main chain is greater than that of the side chains. Instead, this term relates to the composition of this chain. While the side chain has very high proportions of olefinic repeat units, especially units which are derived from alkenes or alkadienes, for example ethylene, propylene, n-butene, isobutene, butadiene, isoprene, the main chain comprises relatively large proportions of polar unsaturated monomers which have been detailed above.

The term “repeat unit” is known to those skilled in the art. The comb polymers can be obtained by a process which involves the free-radical polymerisation of macromonomers and low molecular weight monomers, wherein double bonds are opened up to form covalent bonds. Accordingly, the repeat unit arises from the monomers used. However, the comb polymers can also be prepared by polymer-analogous reactions and graft copolymerisation. In this case, the converted repeat unit of the main chain is counted as a repeat unit which is derived from a polyolefin-based macromonomer. The same applies in the case of preparation of the comb polymers by graft polymerization.

Further details of preparation methods of comb polymers can be found in US2010/0190671 and US2008/0194443, both incorporated herein by reference.

The comb polymers preferred for use in the present invention comprise repeat units which are derived from polyolefin-based macromonomers. These repeat units comprise at least one group which is derived from polyolefins. Examples of suitable polyolefins include C₂-C₁₀ alkenes, such as ethylene, propylene, n-butene, isobutene, norbornene, and/or C₄-C₁₀ alkadienes such as butadiene, isoprene, norbornadiene, and the like.

The repeat units derived from polyolefin-based macromonomers preferably comprise at least 70% by weight and more preferably at least 80% by weight and most preferably at least 90% by weight of groups which are derived from alkene and/or alkadienes, based on the weight of the repeat units derived from polyolefin-based macromonomers.

The polyolefinic groups may also be present in hydrogenated form. In addition to the groups which are derived from alkenes and/or alkadienes, the repeat units derived from polyolefin-based macromonomers may comprise further groups. These include small proportions of copolymerizable monomers, including among others, alkyl (meth)acrylates, styrene monomers, fumurates, maleates, vinyl esters and/or vinyl ethers. The proportion of these groups based on copolymerizable monomers is preferably at most 30% by weight, more preferably at most 15% by weight, based on the weight of the repeat units derived from polyolefin-based macromonomers. The repeat units derived from polyolefin-based macromonomers may comprise start groups and/or end groups which serve from functionalization or are caused by the preparation of the repeat units derived from polyolefin-based macromonomers. The proportion of these start groups and/or end groups is preferably at most 30% by weight, more preferably at most 15% by weight, based on the weight of the repeat units derived from polyolefin-based macromonomers.

The number-average molecular weight of the repeat units which are derived from polyolefin-based macromonomers is preferably in the range from 500 to 50000 g/mol, more preferably from 700 to 10000 g/mol, even more preferably from 1500 to 4900 g/mol and most preferably from 2000 to 3000 g/mol.

The melting point of the repeat units derived from the polyolefin-based macromonomers is preferably less than or equal to −10° C., more preferably less than or equal to −20° C., even more preferably less than or equal to −40° C., as measured by DSC. Most preferably, no DSC melting point can be measured for the repeat units derived from the polyolefin-based macromonomers.

In addition to the repeat units which are derived from the polyolefin-based macromonomers, the comb polymers useful herein comprise repeat units which are derived from low molecular weight monomers selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl(meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, di(alkyl) fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers.

The molecular weight of the low molecular weight repeat units or of the low molecular weight monomers is preferably at most 400 g/mol, more preferably at most 200 g/mol and most preferably at most 150 g/mol.

Examples of styrene monomers having 8 to 17 carbon atoms are styrene, substituted styrenes having an alkyl substituent in the side chain, for example, alpha-methyl-styrene and alpha-ethyl-styrene, substituted styrenes having an alkyl substituent on the ring, such as vinyltoluene p-methylstyrene, halogenated styrenes, for example monochlorostyrenes, dichlorostyrenes, tribromostyrenes, and tetrabromostyrenes.

The term “(meth)acrylates” encompasses acrylates and methacrylates, and also mixtures of acrylates and methacrylates. The alkyl (meth)acrylates having 1 to 10 carbon atoms in the alcohol group include (meth)acrylates which are derived from saturated alcohols, such as methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, tert-butyl(meth)acrylate, pentyl(meth)acrylate, hexyl(meth)acrylate, 2-ethyl-hexyl(meth)acrylate, heptyl(meth)acrylate, 2-tert-butylheptyl(meth)acrylate, octyl(meth)acrylate, 3-isopropylheptyl(meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate; (meth)acrylates which derive from unsaturated alcohols, for example 2-propynyl (meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, oleyl(meth)acrylate; cycloalkyl(meth)acrylates such as cyclpentyl(meth)acrylate, and 3-vinylcyclohexyl(meth)acrylate.

Preferred alkyl(meth)acrylates include 1 to 8, more preferably 1 to 4 carbon atoms in the alcohol group. The alcohol group here may be linear or branched.

Examples of vinyl esters having 1 to 11 carbon atoms in the acyl group include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate. Preferred vinyl esters include 2 to 9, more preferably 2 to 5 carbon atoms in the acyl group. The acyl group may be linear or branched. Examples of vinyl ethers having 1 to 10 carbon atoms in the alcohol group include vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, vinyl butyl ether. Preferred vinyl ethers include 1 to 8, more preferably 1 to 4 carbon atoms in the alcohol group. The alcohol group may be linear or branched.

The term “(di)ester” as used herein means that monoesters, diesters and mixtures of esters, especially of fumaric acid and/or of maleic acid may be used. The (di) alkyl fumurates having 1 to 10 carbon atoms in the alcohol group include monomethyl fumurate, dimethyl fumurate, monoethyl fumurate, diethyl fumurate, methyl ethyl fumurate, monobutyl fumurate, dibutyl fumurate, dipentyl fumurate and dihexyl fumurate. Preferred (di)alkyl fumurates comprise 1 to 8, more preferably 1 to 4, carbon atoms in the alcohol group. The alcohol group may be linear or branched.

The di(alkyl) maleates having 1 to 10 carbon atoms in the alcohol group include monomethyl maleate, dimethyl maleate, monoethyl maleate, diethyl maleate, methyl ethyl maleate, monobutyl maleate, dibutyl maleate. Preferred (di)alkyl maleates comprise 1 to 8, more preferably 1 to 4 carbon atoms in the alcohol group. The alcohol group herein may be linear or branched.

In addition to the repeat units detailed above, the comb polymers useful herein may comprise further repeat units which are derived from further comonomers, their proportion being at most 20% by weight, preferably at most 10% by weight and more preferably at most 5% by weight, based on the weight of the repeat units.

These also include repeat units which are derived from alkyl(meth)acrylates having 11 to 30 carbon atoms in the alcohol group, especially undecyl(meth)acrylate, 5-methylundecyl(meth)acrylate, dodecyl(meth)acrylate, 2-methyldodecyl(meth)acrylate, tridecyl(meth)acrylate, 5-methyltridecyl(meth)acrylate, tetradecyl(meth)acrylate, pentadecyl(meth)acrylate, hexadecyl(meth)acrylate, 2-methylhexadecyl(meth)acrylate, heptadecyl(meth)acrylate, 5-isopropylheptadecyl(meth)acrylate, 4-tert-butyloctadecyl(meth)acrylate, 5-ethyloctadecyl(meth)acrylate, 3-isopropyloctadecyl(meth)acrylate, octadecyl(meth)acrylate, nonadecyl(meth)acrylate, eicosyl(meth)acrylate, cetyleicosyl(meth)acrylate, stearyleicosyl(meth)acrylate, docosyl(meth)acrylate and/or eicosyltetratriacontyl(meth)acrylate.

These also include repeat units which are derived from dispersing oxygen- and nitrogen-functionalized monomers such as those listed in paragraphs [0036]-[0059] of US2010/0190671, incorporated herein by reference.

The comb polymers suitable for use herein preferably have a molar degree of branching in the range of from 0.1 to 10 mol %, more preferably from 0.3 to 6 mol %, even more preferably from 0.3 to 1.1 mol %, especially from 0.4 to 1.0 mol % and most preferably from 0.4 to 0.6 mol %.

The molar degree of branching of the comb polymers f_(branch) is calculated by the formula:

$f_{branch} = \frac{\sum\limits_{a = 1}^{A}n_{a}}{{\sum\limits_{a = 1}^{A}n_{a}} + {\sum\limits_{b = 1}^{B}n_{b}}}$

where:

A is the number of types of repeat units which are derived from polyolefin-based macromonomers,

B is the number of types of repeat units which are derived from low molecular weight monomers selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl(meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers,

n_(a) is the number of repeat units which are derived from polyolefin-based macromonomers of the type a in the comb polymer molecule,

n_(b) is the number of repeat units which are derived from low molecular weight monomers selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl(meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers, of type b in the comb polymer molecule.

The molar degree of branching arises generally from the ratio of the monomers used if the comb polymer has been prepared by copolymerization of low molecular weight and macromolecular monomers. For the calculation, it is possible here to use the number-average molecular weight of the macromonomer.

If the comb polymer has been obtained by polymer-analogous reaction or by grant copolymerization, the molar degree of branching is found by known methods of determining the conversion.

The proportion of at least 80% by weight, preferably at least 90% by weight, of low molecular weight repeat units which are derived from monomers selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl (meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers, and of repeat units which are derived from polyolefin-based macromonomers, is based on the weight of the repeat units. In addition to the repeat units, polymers generally also comprise start groups and end groups which can form through initiation reactions and termination reactions. In one aspect of the present invention, the statement of at least 80% by weight, preferably at least 90% by weight, of low molecular weight repeat units which are derived from monomers selected from the group consisting of styrene monomers having 8 to 17 carbon atoms, alkyl (meth)acrylates having 1 to 10 carbon atoms in the alcohol group, vinyl esters having 1 to 11 carbon atoms in the acyl group, vinyl ethers having 1 to 10 carbon atoms in the alcohol group, (di)alkyl fumurates having 1 to 10 carbon atoms in the alcohol group, (di)alkyl maleates having 1 to 10 carbon atoms in the alcohol group, and mixtures of these monomers, and of repeat units which are derived from polyolefin-based macromonomers, is based on the weight of the comb polymers.

A preferred comb polymer for use herein has 8 to 30% by weight, more preferably 10 to 26% by weight, of repeat units which are derived from polyolefin-based macromonomers, based on the total weight of the repeat units.

Preferred comb polymers for use herein include those which have a weight average molecular weight Mw in the range of 500,000 to 1,000,000 g/mol, more preferably 100,000 to 500,000 g/mol and most preferably 150,000 to 450,000 g/mol.

The number-average molecular weight Mn, may preferably be in the range of 20,000 to 800,000 g/mol, more preferably 40,000 to 200,000 g/mol and most preferably 50,000 to 150,000 g/mol.

Preferably comb polymers used herein have a polydispersity index Mw/Mn in the range of 1 to 5, more preferably in the range of from 2.5 to 4.5. The number average and the weight average molecular weight can be determined by known processes such as Gas Permeation Chromatography (GPC).

In a particular aspect of the present invention, a preferred comb polymer has a low proportion of olefinic double bonds. The iodine number is preferably less than or equal to 0.2 g per g of comb polymer, more preferably less than or equal to 0.1 g per g of comb polymer. This proportion can be determined according to DIN 53241 after drawing off carrier oil and low molecular weight residual monomers at 180° C. under reduced pressure for 24 hours.

In a preferred embodiment herein the lubricating composition comprises a comb polymer having repeat units which are derived from n-butyl methacrylate and/or from n-butyl acrylate. Preferably, the proportion of repeat units which are derived from n-butyl methacrylate and/or from n-butyl acrylate is at least 50% by weight, more preferably at least 60% by weight, based on the total weight of repeat units.

In a preferred embodiment herein the comb polymer has repeat units which are derived from styrene. The proportion of repeat units which are derived from styrene are preferably in the range of 0.1 to 30% by weight, more preferably 5 to 25% by weight.

In a preferred embodiment herein, the comb polymers have repeat units which are derived from alkyl(meth)acrylate having 11-30 carbon atoms in the alkyl radical, preferably in an amount in the range of 0.1% to 15% by weight, more preferably in the range of 1 to 10% by weight.

In a preferred embodiment herein the comb polymer has repeat units which are derived from styrene and repeat units which are derived from n-butyl methacrylate. The weight ratio of styrene repeat units and n-butylmethacrylate repeat units is preferably in the range of 1:1 to 1:9, more preferably 1:2 to 1:8.

In another preferred embodiment, the comb polymer has repeat units which are derived from methyl methacrylate and repeat units which are derived from n-butyl methacrylate, preferably in a weight ratio of 1:1 to 0:100, more preferably 3:7 to 0:100.

A commercially available comb polymer suitable for use herein is available from Evonik Industries under the tradename Viscoplex 3-201.

In another embodiment, the polymeric viscosity index improver is selected from those having 1 to 70 mol % of one or more (meth)acrylate structural units represented by formula (1) below.

In formula (1), R¹ is hydrogen or a methyl group and R² is a straight or branched hydrocarbon group having not less than 16 carbon atoms, preferably not less than 18 carbon atoms, more preferably not less than 20 carbon atoms, and even more preferably a branched hydrocarbon group having not less than 20 carbon atoms.

Said poly(meth)acrylate viscosity index improvers may be either non-dispersant or dispersant type, but the latter is more preferred.

In poly(meth)acrylate viscosity index improvers, the proportion of the (meth)acrylate structural unit represented by formula (1) is preferably 1 to 70 mol %, more preferably not more than 60 mol %, still more preferably not more than 50 mol %, particularly preferably not more than 40 mol %, and especially not more than 30 mol %; and preferably not less than 3 mol %, more preferably not less than 5 mol % and even more preferably not less than 10 mol %.

Said poly(meth)acrylate VI improvers may preferably be a copolymer of one or more monomers represented by formula (2) and a monomer other than that represented by formula (2).

In Formula (2) R¹ is hydrogen or a methyl group and R² is a straight or branched hydrocarbon group having not less than 16 carbon atoms.

Any monomer may be combined with the monomer of formula (2), and for example, a monomer represented by formula (3) below is preferred.

A copolymer of formula (2) and formula (3) is a non-dispersant type poly(meth)acrylate VI improver.

In formula (3), R³ is hydrogen or a methyl group, and R⁴ is a straight or branched hydrocarbon group having 1 to 15 carbon atoms.

As the other monomer to be combined with a monomer of formula (2), one or more of a monomer represented by formula 4 or formula 5 are preferred.

In formula 4, R⁵ is hydrogen or a methyl group, R⁶ is an alkylene group having from 1 to 18 carbon atoms, E¹ is an amine or heterocyclic residue having 1 to 2 nitrogen atoms and 0 to 2 oxygen atoms, and denotes 0 or 1.

In formula 5, R⁷ is hydrogen or a methyl group, E² stands for an amine or heterocyclic residue having 1 to 2 nitrogen atoms and 0 to 2 oxygen atoms.

A copolymer of monomers having formula (2), formula (4) and formula (5) constitutes a dispersant type poly(meth)acrylate VI improver. This dispersant type poly(meth)acrylate VI improver can additionally contain monomer of formula (3) as a constituent monomer.

Specific examples of the R⁶ alkylene group in formula (4) may include ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, tridecylene, tetradecylene, pentadecylene, hexadecylene, heptadecylene, and octadecylene groups (these alkylene groups may be either be straight or branched).

The group represented by E¹ in formula (4) and the group represented by E² in formula (5) may independently be a dimethylamino, diethylamino, dipropylamino, dibutylamino, aniline, toluidino, xylidino, acetylamino, benzoylamino, morpholino, pyrrolyl, pyrrolino, pyridyl, methylpyridyl, pyrrolidinyl, pyperidinyl, quinonyl, pyrrolidonyl, pyrrolidono, imidazolino, or pyrazino group.

Preferred examples of monomers having formula (4) and (5) may include dimethylaminomethyl methacrylate, diethylaminomethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-methyl-5-vinylpyridine, morpholinomethyl methacrylate, morphorinoethyl methacrylate, N-vinylpyrrolidone, and mixtures thereof.

The copolymerisation molar ratio for a copolymer of monomers having formula 2 and formulae 3 to 5 is not particularly limited, and monomer of formula 2: monomer of formulae 3 to 5 is preferably 10:90 to 40:60.

The VI improver may be prepared, for example by radical solvent polymerisation of a mixture of monomers of formula (1) and formulae (3)-(5) in the presence of a polymerisation initiator such as benzoyl peroxide.

As used herein “PSSI” means permanent shear stability index of a polymer calculate from the data measured in accordance with ASTM D 6278-02 with reference to ASTM D 6022-01.

The PSSI of said poly(meth)acrylate VI improver is preferably not more than 35, more preferably not more than 30, even more preferably not more than 25; and preferably not less than 5, more preferably not less than 10, and still more preferably less than 20, and especially not less than 20.

The weight average molecular weight (M_(w)) of the poly(meth)acrylate VI improver is preferably not less than 10,000, more preferably not less than 50000, even more preferably not less than 100000, still more preferably not less than 150000, and most preferably not less than 200000; and preferably not more than 1000000, more preferably not more than 700000, still more preferably not more than 600000, and particularly preferably not more than 500000.

The ratio of the weight average molecular weight to the number average molecular weight for the poly(meth)acrylate VI improver is preferably 0.5 to 5.0, more preferably from 1.0 to 3.5, even more preferably from 1.5 to 3, and especially from 1.7 to 2.5.

The ratio of the weight average molecular weight to the PSSI of the poly(meth)acrylate VI improver is preferably not less than 0.8×10⁴, more preferably not less than 1×10⁴, even more preferably not less than 2×10⁴, and still more preferably not less than 2.5×10⁴.

Examples of suitable poly(meth)acrylate viscosity index improvers for use herein include those disclosed and exemplified in US2011/0124536.

A commercially available poly(meth)acrylate polymer suitable for use herein is available from Sanyo Chemicals under the tradename Aclube 5110.

Another suitable polymeric viscosity index improver for use herein is a styrene-diene hydrogenated copolymer.

An example of a commercially available styrene-diene hydrogenated copolymer suitable for use herein is that available from Infineum under the tradename Infineum SV600.

In preferred embodiments herein the weight ratio of the one or more polymeric viscosity index improvers to the one or more monoesters or mixtures of monoesters is in the range of from 1:8 to 1:40, more preferably in the range of from 1:10 to 1:30.

Typically the lubricating compositions of the present invention would be utilised in, but not necessarily limited to, SAE J300 viscosity grades 0W-16, 0W-20, 0W-30, 0W-40, 5W-20, 5W-30 and 5W-40 as these are the grades which target fuel economy. As new SAE J300 viscosity grades are published, with lower viscosities than the current 0W-16, the present invention would also be very much applicable to these new viscosity lower grades. It is conceivable that the present invention could also be used with higher viscosity grades.

The lubricating composition according to the present invention preferably has a Noack volatility (according to ASTM D 5800) of below 15 wt. %. Typically, the Noack volatility (according to ASTM D 5800) of the composition is between 1 and 15 wt. %.

The lubricating composition according to the present invention further comprises one or more additives such as anti-oxidants, anti-wear additives, dispersants, detergents, overbased detergents, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, metal passivators, corrosion inhibitors, demulsifiers, anti-foam agents, seal compatibility agents and additive diluent base oils, etc.

As the person skilled in the art is familiar with the above and other additives, these are not further discussed here in detail. Specific examples of such additives are described in for example Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 14, pages 477-526.

Anti-oxidants that may be conveniently used include phenyl-naphthylamines (such as “IRGANOX L-06” available from Ciba Specialty Chemicals) and diphenylamines (such as “IRGANOX L-57” available from Ciba Specialty Chemicals) as e.g. disclosed in WO 2007/045629 and EP 1 058 720 B1, phenolic anti-oxidants, etc. The teaching of WO 2007/045629 and EP 1 058 720 B1 is hereby incorporated by reference.

Anti-wear additives that may be conveniently used include zinc-containing compounds such as zinc dithiophosphate compounds selected from zinc dialkyl-, diaryl- and/or alkylaryl-dithiophosphates, molybdenum-containing compounds, boron-containing compounds and ashless anti-wear additives such as substituted or unsubstituted thiophosphoric acids, and salts thereof.

Examples of such molybdenum-containing compounds may conveniently include molybdenum dithiocarbamates, trinuclear molybdenum compounds, for example as described in WO 98/26030, sulphides of molybdenum and molybdenum dithiophosphate.

Boron-containing compounds that may be conveniently used include borate esters, borated fatty amines, borated epoxides, alkali metal (or mixed alkali metal or alkaline earth metal) borates and borated overbased metal salts.

The dispersant used is preferably an ashless dispersant. Suitable examples of ashless dispersants are polybutylene succinimide polyamines and Mannich base type dispersants.

The detergent used is preferably an overbased detergent or detergent mixture containing e.g. salicylate, sulphonate and/or phenate-type detergents.

Examples of other types of viscosity index improvers which may conveniently be used in the lubricating composition of the present invention include the styrene-butadiene stellate copolymers, styrene-isoprene stellate copolymers and the polymethacrylate copolymer and ethylene-propylene copolymers (also known as olefin copolymers) of the crystalline and non-crystalline type. Dispersant-viscosity index improvers may be used in the lubricating composition of the present invention.

Preferably, the composition contains at least 0.1 wt. % of a pour point depressant. As an example, alkylated naphthalene and phenolic polymers, polymethacrylates, maleate/fumarate copolymer esters may be conveniently used as effective pour point depressants. Preferably not more than 0.3 wt. % of the pour point depressant is used. Furthermore, compounds such as alkenyl succinic acid or ester moieties thereof, benzotriazole-based compounds and thiodiazole-based compounds may be conveniently used in the lubricating composition of the present invention as corrosion inhibitors.

Compounds such as polysiloxanes, dimethyl polycyclohexane and polyacrylates may be conveniently used in the lubricating composition of the present invention as defoaming agents.

Compounds which may be conveniently used in the lubricating composition of the present invention as seal fix or seal compatibility agents include, for example, commercially available aromatic esters.

The lubricating compositions of the present invention may be conveniently prepared by admixing the base oil comprising the one or more monoesters or mixture of monoesters and the polymeric viscosity index improver together with, optionally, one or more additives.

The above-mentioned additives are typically present in an amount in the range of from 0.01 to 35.0 wt. %, based on the total weight of the lubricating composition, preferably in an amount in the range of from 0.05 to 25.0 wt. %, more preferably from 1.0 to 20.0 wt. %, based on the total weight of the lubricating composition.

Preferably, the composition contains at least 9.0 wt. %, preferably at least 10.0 wt. %, more preferably at least 11.0 wt % of an additive package comprising an anti-wear additive, a metal detergent, an ashless dispersant and an anti-oxidant.

The lubricating compositions according to the present invention may be so-called “low SAPS” (SAPS=sulphated ash, phosphorus and sulphur), “mid SAPS” or “regular SAPS” formulations.

For Passenger Car Motor Oil (PCMO) engine oils the above ranges mean:

a sulphated ash content (according to ASTM D 874) of up to 0.5 wt. %, up to 0.8 wt. % and up to 1.5 wt. %, respectively;

a phosphorus content (according to ASTM D 5185) of up to 0.05 wt. %, up to 0.08 wt. % and typically up to 0.1 wt. %, respectively; and

a sulphur content (according to ASTM D 5185) of up to 0.2 wt. %, up to 0.3 wt. % and typically up to 0.5 wt. %, respectively.

For Heavy Duty Diesel Engine Oils the above ranges mean:

a sulphated ash content (according to ASTM D 874) of up to 1 wt. %, up to 1 wt. % and up to 2 wt. %, respectively;

a phosphorus content (according to ASTM D 5185) of up to 0.08 wt. % (low SAPS) and up to 0.12 wt. % (mid SAPS), respectively; and

a sulphur content (according to ASTM D 5185) of up to 0.3 wt. % (low SAPS) and up to 0.4 wt. % (mid SAPS), respectively.

In another aspect, the present invention provides the use of a lubricating composition according to the present invention as an engine oil in the crankcase of an engine, in order to improve fuel economy properties. The engine oil may include a heavy duty diesel engine oil, a passenger car motor engine oil, as well as other types of engine oils.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

Examples

The lubricating compositions having the formulations as set out in Table 1 (Examples 1 to 4) are prepared using conventional lubricant preparation methods by combining the GTL base oils and the monoester (Priolube 1544 commercially available from Croda International Plc.) with the additive package and the polymeric viscosity index improver (either the comb polymer Viscoplex 3-201 commercially available from Evonik Industries or the poly(meth)acrylate polymer Aclube V-5110 commercially available from Sanyo Chemicals).

TABLE 1 Example 1 Example 2 Example 3 Example 4 Wt % Wt % Wt % Wt % Additive 12 12 12 12 Package GTL 4¹ 45 0 33.5 0 GTL 8² 9 16 20 25.5 Priolube 25 62 25 52 1544³ Viscoplex 9 10 0 0 3-201⁴ Aclube V- 0 0 9.5 10.5 5110⁵ Total 100 100 100 100 ¹A Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. of approximately 4 cSt which may be conveniently prepared by the process described in WO 02/070631. ²A Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. of approximately 8 cSt which may be conveniently prepared by the process described in WO 02/070631. ³A monoester supplied by Croda International Plc. ⁴A comb polymer supplied by Evonik Industries. ⁵A poly(meth)acrylate VI improver supplied by Sanyo Chemicals.

The lubricating compositions having the formulations as set out in Table 2 (Examples 5 to 12) are prepared using conventional lubricant preparation methods. The monoester used in Examples 8, 9, 11 and 12 was Sample 2 of WO2009/130445. The polymeric viscosity index improvers used in Examples 6-12 were chosen from Viscoplex 3-201 (a comb polymer from Evonik Industries), Aclube 5110 (a poly(meth)acrylate polymer from Sanyo Chemicals) and Infineum SV277 (a styrene-diene hydrogenated copolymer from Infineum).

In order to demonstrate the improved fuel economy properties of the lubricating compositions of the present invention, Examples 5 to 9 were subjected to various test methods, as specified in Table 2 below.

TABLE 2 Example Example Example Example Example Example Example Example 5* 6* 7* 8 9 10* 11 12 Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % Additive 12.1 12.1 12.1 12.1 12.1 12.1 12.1 12.1 Package GTL 4¹ 30.2 78.9 72.9 40.7 0 62.2 28.9 0 GTL 8² 57.7 2 7.3 8 13.6 17 19.5 21.8 Monoester³ 0 0 0 30 64.6 0 30 55.9 Infineum SV 0 7 0 0 0 0 0 0 277⁴ Viscoplex 3- 0 0 7.7 9.2 9.7 0 0 0 201⁵ Aclube 5110⁶ 0 0 0 0 0 8.7 9.5 10.2 Total wt % 100 100 100 100 100 100 100 100 kV100 (mm²/s)⁷ 7.92 9.05 7.4 7.7 7.61 8.2 8.35 8.47 kV40 (mm²/s)⁸ 45.55 45.12 32.8 29.4 25.9 31.9 30.4 29.1 VI⁹ 146 187 202 248 291 249 272 293 CCS at −35° C. 9365 3954 4152 2473 1450 2686 1724 1176 (cP)¹⁰ HTHS 100 6.25 5.6 5.26 5.08 4.87 4.91 4.79 4.69 (cP)¹¹ HTHS 150 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 (cP)¹² Noack 4.75 13.5 13.5 13.5 13.5 13.5 13.5 13.5 evaporation loss (wt %)¹³ M111 FE Test Not 3.56 4.31 4.90 Not 4.36 Not Not (%)¹⁴ measured measured measured measured *Comparative Examples ¹A Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. of approximately 4 cSt which may be conveniently prepared by the process described in WO 02/070631 ²A Fischer-Tropsch derived base oil having a kinematic viscosity at 100° C. of approximately 8 cSt which may be conveniently prepared by the process described in WO 02/070631 ³Sample 2 of WO2009/130445 ⁴Styrene-diene hydrogenated copolymer commercially available from Infineum ⁵Comb polymer supplied by Evonik Industries ⁶Poly(meth)acrylate copolymer supplied by Sanyo Chemicals ⁷Kinematic viscosity at 100° C. as measured according to ASTM D445 ⁸Kinematic viscosity at 40° C. as measured according to ASTM D445 ⁹Viscosity Index as calculated according to ASTM D2270 ¹⁰Cold crank simulation (CCS) dynamic viscosity (according to ASTM D5293) at −35° C. ¹¹High Temperature/High Shear viscosity at 100° C. as measured according to ASTM D6616 ¹²High Temperature/High Shear viscosity at 150° C. as measured according to ASTM D4683 ¹³Noack evaporation loss as measured according to ASTM D5800 ¹⁴Fuel economy test method according to CEC L-54-T-96

DISCUSSION

It can be seen from Table 2 that, for the given HTHS 150 (2.6), addition of a polymeric VI improver increases the VI and reduces the HTHS 100.

By selecting a comb polymer (such as Viscoplex 3-210) or a poly(meth)acrylate polymer with optimised architecture (such as Aclube 5110), the VI is higher and the HTHS 100 is lower. This translates to improved fuel economy (as seen in Comparative Example 7 and Example 10).

On addition of the monoester (Example 4 and 5, and Examples 7 and 8), the VI further increases and the HTHS 100 reduces. This translates to improved fuel economy (as seen in Example 8 compared with Comparative Example 7).

As an engine operates closer to 100° C. than 150° C., the lubricant is thinner in operating conditions and therefore delivers improved fuel economy. 

1. A lubricating composition for use in the crankcase of an engine comprising: (i) a base oil comprising at least one monoester or a mixture of monoesters, wherein said monoester or mixture of monoesters has a kinematic viscosity at 100° C. of not more than 4 mm²/s, a viscosity index of at least 130 and a Noack evaporation loss of not more than 20 wt %; and (ii) a polymeric viscosity index improver selected from (a) one or more comb polymers; (b) a poly (meth) acrylate polymer having 1 to mol % of one or more (meth) acrylate structural units represented by formula (1) below

wherein R¹ is a hydrogen atom or a methyl group, and R² is a straight chain or branched hydrocarbon group having not less than 16 carbon atoms; (c) styrene-diene hydrogenated copolymers; and (d) mixtures thereof.
 2. A lubricating composition according to claim 1 wherein said monoester or mixtures of monoesters has a kinematic viscosity at 100° C. of not more than 3.3 mm²/s.
 3. A lubricating composition according to claim 1 wherein said monoester or mixtures of monoesters has a Noack evaporation loss of not more than 15 wt %.
 4. A lubricating composition according to claim 1 wherein the at least one monoester or mixture of monoesters is present at a total level of at least 10 wt %, by weight of the lubricating composition.
 5. A lubricating composition according to claim 1 wherein the at least one monoester or mixture of monoesters is present at a total level of at most 75 wt %, by weight of the lubricating composition.
 6. A lubricating composition according to claim 1 wherein the polymeric viscosity index improver is a comb polymer.
 7. A lubricating composition according to claim 1 wherein the polymeric viscosity index improver is present in a solid polymer amount of from 0.1 wt % to 7 wt %, by weight of the lubricating composition.
 8. A lubricating composition according to claim 1 wherein said at least one monoester or mixture of said monoesters has a non-polarity index of at least
 90. 9. A lubricating composition according to claim 1 wherein said at least one monoester or mixture of said monoesters has a pour point of not more than −30° C.
 10. A lubricating composition according to claim 1 wherein said at least one monoester, or mixture of said monoesters has a kinematic viscosity at 100° C. of not more than 3.0 cSt and/or a viscosity index of at least 140 and/or a pour point of not more than −35° C. and/or a Noack evaporation loss of not more than 15.0 wt %.
 11. A lubricating composition according to claim 1 wherein said at least one monoester is the reaction product of a monohydric alcohol and a monocarboxylic acid wherein said monohydric alcohol is at least one saturated branched-chain aliphatic monohydric alcohol having between 16 and 36 carbon atoms and wherein said monocarboxylic acid is at least one saturated straight-chain aliphatic monocarboxylic acid having between 5 and 10 carbon atoms.
 12. A lubricating composition according to claim 11 wherein said alcohol comprises an alcohol branched at the β position on the main carbon chain and which contains 20 carbon atoms.
 13. A lubricating composition according to claim 11 wherein said acid is pentanoic acid and/or heptanoic acid.
 14. A lubricating composition according to claim 1 wherein the base oil additionally comprises a Fischer-Tropsch derived base oil.
 15. A method comprising: applying a lubricating composition according to claim 1 to a surface in the crankcase of an engine. 